Embodiments presented herein relate generally to displacement sensors, and more specifically to optical displacement sensors.
Displacement sensors are used to sense and measure displacement of an object relative to another object, or the mean position of the object. Displacement sensors may be used to measure vibration intensity and frequency of the object being monitored. One known type of displacement sensor is the linear variable differential transformer (LVDT) based displacement sensor. An LVDT typically has three solenoid coils disposed end-to-end around a shaft—a primary coil at the middle, and two secondary coils on both sides of the primary coil. Displacement is measured as a differential signal generated due to changes in mutual inductance linked with the secondary coils. A cylindrical ferromagnetic core attached to a shaft moves between the solenoid coils based on displacement of the shaft. The shaft is held in its mean position by a spring mechanism. Sensitivity and calibration of LVDT type displacement sensors depend primarily on the spring mechanism. Therefore, the sensor performance depends primarily on the manufacturing tolerance the spring mechanism, and coupling of the shaft to the spring mechanism.
In the medical community, displacement sensors may be used, for example, to monitor frequency and strength of uterine contractions of pregnant women, during delivery. Such a device is known as a tocodynamometer. In tocodynamometers, a membrane is coupled to the LVDT shaft, for accepting displacement inputs from, for example, the abdominal wall of the patient. With time, the membrane, and the spring mechanism experience permanent deformation, thus adversely affecting the sensitivity and calibration of the tocodynamometer.
While displacement sensors are known in the art, what is needed is a displacement sensor that overcomes these and other shortcomings associated with known displacement sensors.